Development apparatus

ABSTRACT

Apparatus for producing facsimile copies having high resolution and uniformity from electrostatically charged latent images on a dielectric support member in which a quantity of developer material comprising a uniformly dispersed toner material is transported into transfer relation with the dielectric support member having the latent electrostatic images thereon. The developer material which includes a magnetically attractable carrier material is supported on the applicator member by means of an attractive force generated by a suitable magnetic field. The toner is maintained at a uniformly dispersed concentration in the developer material by means of concentrically arranged screw conveyor members which provide a continuously recirculated supply of developer material in position to be attracted to the cylindrical applicator member.

United States Patent 172] Inventors Gerald A. Buddendeck Rochester; Robert J. Kelsch, Henrietta, both of, N.Y. [21] Appl. No. 759,178 [22] Filed Sept. 11, 1968 [45] Patented June 8, 1971 173] Assignee Xerox Corporation Rochester, N.Y.

[54] DEVELOPMENT APPARATUS 6 Claims, 5 Drawing Figs.

[52] US. Cl 118/637, 1 17/ 17.5 [51] Int. Cl B05b 5/02 [50] Field of Search 118/637; 1 17/ 17.5

[56] References Cited UNITED STATES PATENTS 3,117,884 1/1964 Greig 117/]7.5 3,l45,122 8/1964 Streich, Sr. 118/637 3,399,652 9/1968 Gawron ABSTRACT: Apparatus for producing facsimile copies having high resolution and uniformity from electrostatically charged latent images on a dielectric support member in which a quantity of developer material comprising a uniformly dispersed toner material is transported into transfer relation with the dielectric support member having the latent electrostatic images thereon. The developer material which includes a magnetically attractable carrier material is supported on the applicator member by means of an attractive force generated by a suitable magnetic field. The toner is maintained at a uniformly dispersed concentration in the developer material by means of concentrically arranged screw conveyor members which provide a continuously recirculated supply of developer material in position to be attracted to the cylindrical applicator member.

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DEVELOPM ENT APPARATUS BACKGROUND OF THE INVENTION This invention relates generally to apparatus for developing electrostatically charged latent images and more particularly to apparatus for applying developer powder or toner to electrostatically charged latent images on a dielectric support member.

In the art of electrographic recording, a pattern of electrostatic charges is placed on a suitable dielectric support material in a configuration corresponding to the desired information record. This pattern of electrostatic charges may be applied directly to the recording surface by an electrographic recording stylus, an electrode array, or any of the other known electrographic recording means. Subsequently, the charge pattern is developed or toned by a suitable toner material which may comprise a pigmented thermoplastic resin. Subsequent to the development process, the toner material on the dielectric support member is fused to the support to form a permanent copy of the information.

The process of electrographic recording in some aspects is similar to the now well known xerographic process. That is, in both processes patterns of electrostatic charges are created which correspond to the desired information record. In the process of xerography, this is accomplished by blanket charging of a photoconductive insulator, and then selectively discharging portions thereof by exposure to light, generally through a suitable optical system. However, the process of electrographic recording differs from the process of xerography in that the charge pattern in electrographic recording is created without the use of photosensitive materials. That is, the process of xerography requires the use of a suitable photoconductor, whereas the process of electrographic recording does not.

An apparatuswhich utilizes the electrographic recording process is that which is disclosed in copending application, Ser. No. 758,932 filed concurrently herewith in the names of I-Ialbert M. Harris et al. and assigned to the same assignee as the instant invention. As described therein, electrographic recording styli are utilized to apply a charge pattern in image configuration to a suitable dielectric recording medium. As the styli are traversed relative to the support medium, one suitable medium being for example ordinary cut sheet paper stock, a suitably high voltage or potential is applied across the dielectric recording medium to produce a latent residual charge pattern of graphic information. In the particular apparatus referred to above, an electrical signal is generated as a result of the scanning of a document at another location by measuring reflected light levels of the information thereon. This electrical signal is then utilized to control the voltage or potential applied to the styli at any point in time representative of the reflectivity of a dot or small portion of the scanned information. Thus, for example, if an applicably high voltage is applied to the styli by an electronic drive circuit, a residual voltage proportionate to the applied voltage level will remain on the surface of the dielectric, the residual voltage however decaying with time and as a function of ambient conditions.

In comparison to the residual voltages retained on a photoconductor in the xerographic process, the residual voltage retained on the dielectric support member in the electrographic recording process are generally of substantially lesser magnitudes. Because of the lesser magnitude of retained residual voltages on the surface of the dielectric, the develo ment of the electrographically produced latent images have therefore presented certain problems which have not heretofore been a consideration in the development oflatent electrostatic images produced by xerographic processes.

Accordingly, the development of electrographically produced latent electrostatic images by known xerographic developing apparatus has not produced images to a degree of uniformity and resolution required according to modern day copy quality standards. In contrast, however, the same xerographic developing apparatus has been quite effective for producing copies of the highest possible quality from xerographically produced images.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide improved development apparatus for rendering latent electrostatic images visible.

It is another object of the present invention to provide improved latent electrostatic image development apparatus for producing copies having a high degree of uniformity and resolution from electrographically formed latent electrostatic images.

It is yet another object of the present invention to provide apparatus for effectively rendering latent electrostatic images visible from both electrographically and xerographically formed images.

It is still a further object of the present invention to provide apparatus for developing electrographically produced latent electrostatic images yielding copies having a high degree of uniformity and resolution from relatively low voltage variable density residual charge patterns.

These and other objects of the invention are attained by means of a generally cylindrical applicator member transversely positioned adjacent a copy feed path for transporting developer material into transfer relationship with copy sheets having electrostatic images thereon. The developer material comprising carrier particles having magnetic properties, and electroscopic powders or toners, is supported in the lower portion of a housing member which at the upper portion thereof rotatably supports the cylindrical applicator member. A toner dispensing apparatus is supported at the upper portion of a mixing and supply chamber connected at one end in communication with the housing member for automatically adding a variable predetermined quantity of toner to the developer material as toner is depleted during the development process. The toner and carrier comprising the developer material are continuously mixed by a recirculating conveyor system which transports developer material in a first direction transversely along the copy feed path from the mixing and supply chamber and in a second direction transversely along the copy feed path to return to the mixing and supply chamber.

A first rotatable screw conveyor member extends from within the mixing and supply chamber transversely through the housing member. A second screw conveyor member is mounted concentric with the first conveyor member to rotate therewith. Developer material is thus conveyed from within the mixing and supply chamber transversely through the housing member by the second conveyor member into communication with the first conveyor member which returns the developer material to the mixing and supply chamber. The recirculating conveyor system thus maintains a highly uniform dispersion of toner particles in the carrier material which substantially enhances the quality of development obtained.

A magnetic field is generated by means of a magnetic member adjustably positioned within the cylindrical applicator member whereby the magnetic carrier particles with the uniformly distributed toner particles adhering thereto are attracted to the applicator member to be transported into transfer relation with a charged copy sheet at the development station.

A platen member is positioned above the cylindrical applicator member at the transfer station to provide a support for holding copy sheets in transfer relation with developer material supported on the cylindrical applicator member. The platen member is provided with an electrical bias to produce a charge thereon in opposition to the charge of the toner particles whereby to repel toner particles from the nonimage areas on the copy sheet.

Other objects of the invention will become readily apparent to those skilled in the art in view of the following detailed disclosure and description thereof, especially when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view showing a facsimile transceiver apparatus in which the present invention is particularly adapted for use.

FIG. 2 is a front elevation partly broken away showing the development apparatus according to the present invention.

FIG. 3 is a cross-sectional view taken along the lines 3-3.

FIG. 4 is a partly broken away sectional view taken from the lines 4-4 of FIG. 2.

FIG. 5 is an end elevation showing the drive arrangement for the development apparatus.

In a preferred form of the invention, the developing apparatus is particularly adapted for use in development of electrographically formed latent electrostatic images such as those formed on copy sheets in a facsimile recorder of the type illustrated in copending application, Ser. No. 758,932, filed concurrently herewith in the names of Halbert M. Harris et al. and assigned to the same assignee as the instant invention.

As may be seen from FIGS. 2 and 3, the developing apparatus generally designated 900 is partially enclosed in a housing member 901 supported between frame plates 852 and 853. Housing member 901 includes a mixing and supply chamber 902 connected to housing 901 through frame plate 852. The lower portion of housing member 901 and supply chamber 902 has an internal cross section ofgenerally circular configuration and forms a sump for the developer material utilized in the developer apparatus.

A first conveyor member 903, having one or more helical threads 904 extending thereabout, is rotatably journaled at one end in supply chamber 902, and at the other end thereof in frame plate 853. Conveyor member 903 extends through frame plate 853 by a suitable journal arrangement and has connected thereto a drive sprocket 873 for driving the con veyor assembly.

A second conveyor member 905 having one or more helical threads 906 extending thereabout is supported concentrically about conveyor member 903 and is rigidly connected thereto. The threads 906 on conveyor member 905 run in a direction opposite to the direction of threads 904 on conveyor member 903, the reason for which will hereinafter be more fully described. In the preferred embodiment, the threads on conveyor member 903 extend in the left hand direction while those on conveyor member 905 extend in the right hand direction. Conveyor member 905 is of a shorter axial dimension than that of conveyor member 903 for a reason which will hereinafter become apparent. That is, the ends of conveyor member 905 are spaced from the ends of conveyor member 903 as may be seen in FIG. 2.

A generally cylindrical applicator member 907 is positioned above conveyor member 905 to transport developer material into transfer relation with copy sheets 105. Applicator member 907 is rotatably journaled between frame plates 852 and 853 by a shaft 908 within applicator member 907. Shaft 908 at one end extends through frame plate 852 and at the other end through frame plate 853. A drive sprocket 874 coaxial with the end of shaft 908 extending through frame plate 853 is connected to cylindrical applicator member 907 to provide a drive arrangement for rotating applicator member 907 about shaft 908.

Magnetic members 909 and 909' are supported within cylindrical applicator member 907 by shaft 908. In the preferred embodiment of the invention, magnetic members 909 and 909' comprise a plurality of permanent magnets which are connected to axially extra riding faceted portions of shaft 908. Magnet members 909 and 909 are arranged on shaft 908 to produce a strong magnetic field in the developer pick up area and which extends into the development zone. The arrangement of magnet members 909 and 909 further produces a weaker magnetic field on the discharge side of the development zone which permits developer material to be returned to the reservoir 901. In the preferred arrangement, magnet members 909 extend in a generally vertical direction toward the development zone from shaft 908 Magnet members 909' extend in a generally perpendicular relationship to magnet members 909 from shaft 908, with unlike poles being in adjacent abutting relationship.

Shaft 908 being rotatably journaled with respect to applicator member 907, permits adjustable positioning of the angular displacement of magnet members 909 and 909' about the axis of shaft 908 and cylindrical applicator member 907. A bar member 901, as shown in FIG. 2, is releasably held against the extending end of shaft 908 by means of screws 911 or other suitable fastening means after magnet members 909 and 909' have been displaced to the desired angular position. It has been found that optimum results are attained at an angular displacement of magnet members 909 from a vertical axis through shaft 908 of approximately 15 in the counterclockwise direction as viewed in FIG. 3.

As may be seen from FIG. 3, an upwardly extending transverse plate 912 is attached to the main developer housing by means of bolts 913 or other suitable fastening means. Plate member 912 includes a projecting portion 914 which projects toward the surface of applicator member 907. Plate member 912 with projection 914, thereon may be adjustably positioned a predetermined distance from applicator member 907 to regulate the thickness of developer material on applicator member 907 which is brought into transfer relationship with the copy sheets 105.

A platen member 916 is positioned above applicator member 907 to provide firstly an upper guide member for guiding the leading edges of advancing copy sheets from pinch rollers 862 and 865 past applicator member 907. Platen member 916 secondly serves an additional purpose in the development process in obtaining uniform high quality images without undesirable background areas. A negative bias voltage is applied to platen member 916 which serves to eliminate toner material from adhering to the copy sheets in the background areas.

A generally flat transversely extending plate 915 is positioned below platen 916 at an inclination to provide a lower guide member for guiding the leading edges of advancing copy sheets 105 from pinch rollers 862 and 865 over applicator member 907.

In the preferred embodiment an electrical bias on the platen member 916 is provided which is on the order of 50-100 volts. This negative bias serves to form a repelling force of the negatively charged toner particles. The positively charged image areas on the copy sheet however, are unaffected by this negative bias. Therefore as a result of the negative bias on platen member 916 a repelling force is exerted uniformly against the toner material in both the image and nonimage areas. However, this repelling force is of a lesser magnitude than the attractive forces exerted between the positive charged image areas and the negatively charged toner particles. The toner particles thus are attracted to the image areas to render the images visible.

The developer apparatus 900 may be initially charged with developer material through the open area at the upper front adjacent applicator member 907. Preferably, however, the developer is initially charged with developer material by adding the developer material through supply chamber 902.

Mounted atop supply chamber 902 is an automatic toner dispensing apparatus 920 for automatically adding toner material to the developer supply at an adjustable predetermined rate, as toner material from the developer supply is depleted through the development process. Toner dispensing apparatus 920 is preferably of the type disclosed in Hunt, U.S. Pat. No. 3,0l3,703 and, assigned to Xerox Corporation, Rochester, New York. The dispensing apparatus includes a hopper or container for the toner particles to be dispensed which is preferably fabricated from a material such as sheet metal into a rectangular open-ended box having vertical sidewalls 922 and end walls 923. The hopper or container is closed at the upper end by a door 921 hinged at one side and latched in the closed position at the other side by means of spring dctent 917. At opposite ends of the hopper a e positioned depending bearing blocks or support members 924 and 925 for supporting the dispensing elements of the toner dispenser, the bearing blocks or support members being attached to end walls 923 by screws or other suitable fastening means.

The bottom of the hopper is partially closed by a dispensing plate or platform 926 positioned in spaced vertical relation below the lower edges of the walls of the hopper. The dispensing plate or platform 926 which is as wide as the hopper, may be supported by means of notched extensions of plate 926 engaging mating shoulder portions of support members 924 and 925. The dispensing plate of platform 926 combines with the walls of the hopper to provide a reservoir having narrow elongated discharge outlets or discharge passages 927 along either side for the outflow of toner particles To effect substantially uniform flow of toner particles through the outlets or passages 927 there is provided a metering element 928 having a dispensing grid positioned for reciprocating motion in the space between the dispensing platform 926 and the lower edges of the walls of the hopper. The metering element 928 has a dispensing grid formed by a top wall having a series of transverse perforations or slots formed therein and depending sidewalls 930. The ends of depending sidewalls 930 are bent inward at right angles to form flanges to which support plates 932 are secured as by spot welding.

The metering element 928 is supported by parallel guide rods or rod members 933 extending through holes in support plates 932, the ends of the rod members being supported in apertures formed in bearing blocks 924 and 925. Rod members 933 are adjustably secured to bearing blocks 924 and 925 by set screws or other suitable fastening means and provide a path of movement for the metering element 928 over the dispensing plate 926 as the metering element 928 is reciprocated therealong.

For effecting movement of the metering element, a plunger rod 938 isjournaled in an aperture in mixing chamber 902 and is engageable at the inward end with one of the support plates 932. A pair of compression spring members 929 are encircled about the rod members 933 and abut at opposite ends against the bearing block 925 and support plate 932 to normally bias the metering element to the left as viewed in FIG. 4. Thus as the metering element 928 is biased to the left, plunger rod 938 is likewise normally biased to the left under the influence of springs 929. The metering element is driven to the right as viewed in FIG. 4 to dispense toner therefrom by a drive arrangement from motor MOT-900. Motor MOT-900 is mounted inwardly on frame plate 852 by bolts or other suitable fastening means with the output shaft therefrom extending through frame plate 852 and having connected thereto a spur gear 940. A cam 945, rotatably journaled on stub shaft 944 is engageable with the exterior end of plunger rod 938. A ratchet gear 946 is rotatably journaled on stub shaft 944 and is rigidly connected to cam member 945 in spaced relationship therewith via a drive bushing or other suitable connecting means rotatable on stub shaft 944. A crank arm 943 is rotatably journaled about stub shaft 944 on the drive bushing connecting cam member 945 and ratchet gear 946. A pawl 949 is pivotably supported on pivot pin 947 and resiliently biased into engagement with ratchet gear 946 by means of torsion spring 948. Crank member 943 is connected to spur gear 940 by means of crank pin 941 on spur gear 940, which is engageable with cam slot 942 in crank member 943. Thus as spur gear 940 is rotated under the influence of motor MOT-900, crank member 943 will be pivoted about stub shaft 944 on the connecting bushing member to advance ratchet gear 946 and connected cam member 945. Thus as cam 945 is rotated, plunger rod 938 will be advanced to the right as viewed in FIG. 4 as the contact point between cam member 945 and plunger rod 938 changes from the low to the high point. After reaching the high point on cam 945, plunger rod 938 and dispensing grid 928 will be returned to the position as shown in FIG. 4 under the influence of coil springs 929. Thus as metering element 928 is reciprocated over the dispensing platform 926, toner particles from within the hopper will be dispensed through the outlets or passages 927 into the mixing chamber 902.

A bell crank member 918 is rotatably supported on stub shaft 944 to control the amount that ratchet gear 946 and cam 945 are displaced per stroke of crank member 943 and hence the quantity of toner material dispensed thereby. A spring detent 919 is engageable with notches 920 on bell crank 918 to adjustably secure bell crank 918 to the desired angular position. A projection 921 on bell crank 918 is engageable with pawl 949 whereby to support pawl 949 out of contact with ratchet gear 946 during at least a portion of the advancing stroke of crank member 943. Depending upon the rotative positioning of bell crank 918, the number of teeth which pawl member 949 is permitted to engage on the advancing stroke may be controlled thus controlling the amount of displacement imparted to cam member 945 and hence the quantity of toner dispensed thereby.

A transversely extending drive shaft 871 is rotatably journaled between frame plates 852 and 853 and at one end thereof has connected thereto a spur gear 870 which meshes with spur gear 940 connected to the output shaft of motor MOT900. At the other end of drive shaft 871 is connected a drive sprocket 872 for driving the developer apparatus 900.

Drive sprocket 872 is operatively connected by means of a flexible drive chain 882 to drive sprocket 874 on applicator member 907 and drive sprocket 873 on conveyor members 903 and 905 to drive applicator member 907 in the clockwise direction as viewed in FIG. 3 and conveyor members 903 and 905 both in the counterclockwise direction as viewed in FIG. 3.

As conveyor 903 and concentrically mounted conveyor member 905 are rotated in the counterclockwise direction as viewed in FIG. 3, developer material from within supply chamber 902 will be advanced axially along the outer periphery of conveyor member 905 by means of the helical screw threads extending thereabout. At the same time, once the system has reached the operative or equilibrium condition, developer material will be advanced axially along the outer periphery of conveyor member 903 to within supply chamber 902 by means of the oppositely pitched helical screw threads extending about conveyor member 903. As the conveyor members 905 and 903 are rotated, the developer material is thus continuously mixed and agitated in a recirculating fashion passing from supply chamber 902 advancing both angularly and axially in relation to conveyor member 905 into communication with conveyor member 903, then advancing both angularly and axially in relation to conveyor member 903 into communication with conveyor member 905 in supply chamber 902 whereby to obtain and maintain a highly uniform dispersion of toner particles in the developer mixture.

In addition to the movement of developer material axially along conveyor members 903 and 905, the developer material is angularly transported about the respective conveyor members as a result of the pitch of the screw threads on the respective conveyor members. This arrangement thus provides at all times a quantity of developer material having a uniformly distributed quantity of toner particles therein, in position to be picked up by applicator member 907.

Copy sheets having latent electrostatic images thereon which are to be developed may be transported into transfer relation at the transfer station by means of any suitably arranged transport system. One such system is that disclosed in copending application, Ser. No. 758,932 in which a pair of friction drive rolls such as 862 and 865 advance copy sheets into transfer relation with applicator member 907 at the transfer station.

The arrangement of magnetic members 909 and 909 on shaft 908 produces a magnetic field, the lines of force ofwhich extend about applicator member 907 in the direction toward the input side of the transfer station with a greater effective density or intensity than that which extends about applicator member 907 in the direction toward the output side of the transfer station. Thus as applicator member 907 is rotated, developer material will be continuously attracted toward applicator member 907 to be supported thereon under the influence of the strong magnetic field generated by magnetic members 909 and 909'. As applicator member 907 with developer material supported thereon is rotated toward the copy sheets at the transfer station, the projection 914 on transversely extending plate member 912 serves to act as a doctor blade thus providing a uniform thickness of developer material on applicator member 907 being transported into transfer relation with a copy sheet at the transfer station.

On the applicator member 907, the developer material is supported in a manner generally resembling bristles of a brush. This is the result of the tendency of the magnetic partieles to align with the lines of force ofthe magnetic field. At the transfer station, the lines of force of the magnetic field pass through applicator member 907 approximately normal to the surface thereof as a result of the positioning of magnetic members 909 and 909'. Thus as applicator member 907 with the developer material thereon moves through the stationary magnetic field, the orientation of the brush array with respect to applicator member 907 varies in accordance with the direction of the lines of force of the magnetic field. This therefore produces a movement of the magnetic particles supported on applicator member 907 from a tangential position through a vertical position at the maximum field over the respective poles. At the transfer station, the brush array of developer material on applicator member 907 passes through the strong field directly over the upper pole of magnetic members 909. Thus the developer material is brushed against the surface of a copy sheet supported at the transfer station against platen member 916, under the combined action of the rotation of applicator member 907 and the movement produced by the magnetic field. Due to the fact that the developer material conforms to the surface of applicator member 907 in a pattern generally conforming to the lines of force generated by magnetic members 909, the developer material is brushed against a copy sheet positioned against platen member 916.

On the exit side of the transfer station, due to the arrangement of the magnetic members 909 and 909' and the weaker magnetic field as a result thereof, the developer material is only loosely supported on applicator member 907. Because of this weak magnetic field, much of the developer material falls from the surface of applicator member 907 back to the developer housing. Thus, that developer material from which toner material has been depleted at the transfer station is removed from applicator member 907 and returned to the housing. The developer material which is returned to the supply of developer material in the housing member 901 is then mixed with additional developer material therein by the agitating action imparted by conveyor members 903 and 905.

From the foregoing arrangement it may thus be seen that there is provided an improved developing apparatus which yields copies of exceptionally high resolution and uniformity from electrographically formed latent electrostatic images.

While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the invention without departing from its essential teachings.

What we claim is:

1. Apparatus for developing electrostatically charged latent images of information on a dielectric support member comprising,

a supply chamber for storing a quantity of magnetically attractable developer material comprising magnetic carrier particles and triboelectrically charged toner particles,

:1 housing member in communication with said supply chamber,

a generally cylindrical applicator member rotatably journaled in said housing member for transporting a quantity of developer material from said housing member into transfer relation with a dielectric support member having latent electrostatic images thereon,

magnetic means within said applicator member and adapted to generate a magnetic field whereby to provide an attractive force for supporting a quantity of magnetically attractable developer material from said housing member onto said applicator member,

conveyor means in communication with said supply chamber and said housing member for transporting developer material from within said supply chamber through said housing member and to return to said supply chamber in a recirculating manner whereby to maintain a uniform dispersion of the toner particles within said developer material,

said conveyor means comprising a first cylindrical member having helical threads extending spirally about the periphery thereof for conveying developer material in a first direction through said housing member, and a second generally cylindrical member supported coaxial with said first cylindrical member and having helical threads extending spirally about the periphery thereoffor conveying developer material in a second direction through said housing member, and

means for rotating said first and second cylindrical members about the central axis thereof.

2. Apparatus according to claim 1 wherein,

said first and said second cylindrical members are secured together to rotate in the same angular direction, and

the threads on said first and second cylindrical members are arranged in oppositely extending directions.

3. Apparatus according to claim 2,

said second cylindrical member being in circumambient relationship with said first cylindrical member,

said second cylindrical member advancing developer material from within said supply chamber through said housing member into position to be picked up by said applicator member and into communication with said first cylindrical member, and

said first cylindrical member advancing developer material from within said housing member to within said supply chamber.

4. Apparatus according to claim 1 further including, toner dispensing means in communication with said supply chamber for automatically adding a quantity of toner particles to the developer material at an adjustable predetermined rate.

5. Apparatus according to claim 1 further including, platen means positioned adjacent said applicator member for supporting a dielectric support member having electrostatic latent images thereon in transfer relation therewith, said platen means being electrically biased to a polarity opposite from the polarity of the electrostatic charge patterns on said dielectric support and of the same polarity as the polarity of the toner particles in said developer material.

6. Apparatus according to claim 5, said magnetic means being adjustably positioned within said applicator member to permit selective positioning of said magnetic means in relation to said platen means. 

1. Apparatus for developing electrostatically charged latent images of information on a dielectric support member comprising, a supply chamber for storing a quantity of magnetically attractable developer material comprising magnetic carrier particles and triboelectrically charged toner particles, a housing member in communication with said supply chamber, a generally cylindrical applicator member rotatably journaled in said housing member for transporting a quantity of developer material from said housing member into transfer relation with a dielectric support member having latent electrostatic images thereon, magnetic means within said applicator member and adapted to generate a magnetic field whereby to provide an attractive force for supporting a quantity of magnetically attractable developer material from said housing member onto said applicator member, conveyor means in communication with said supply chamber and said housing member for transporting developer material from within said supply chamber through said housing member and to return to said supply chamber in a recirculating manner whereby to maintain a uniform dispersion of the toner particles within said developer material, said conveyor means comprising a first cylindrical member having helical threads extending spirally about the periphery thereof for conveying developer material in a first direction through said housing member, and a second generally cylindrical member supported coaxial with said first cylindrical member and having helical threads extending spirally about the periphery thereof for conveying developer material in a second direction through said housing member, and means for rotating said first and second cylindrical members about the central axis thereof.
 2. Apparatus according to claim 1 wherein, said first and said second cylindrical members are secured together to rotate in the same angular direction, and the threads on said first and second cylindrical members are arranged in opposiTely extending directions.
 3. Apparatus according to claim 2, said second cylindrical member being in circumambient relationship with said first cylindrical member, said second cylindrical member advancing developer material from within said supply chamber through said housing member into position to be picked up by said applicator member and into communication with said first cylindrical member, and said first cylindrical member advancing developer material from within said housing member to within said supply chamber.
 4. Apparatus according to claim 1 further including, toner dispensing means in communication with said supply chamber for automatically adding a quantity of toner particles to the developer material at an adjustable predetermined rate.
 5. Apparatus according to claim 1 further including, platen means positioned adjacent said applicator member for supporting a dielectric support member having electrostatic latent images thereon in transfer relation therewith, said platen means being electrically biased to a polarity opposite from the polarity of the electrostatic charge patterns on said dielectric support and of the same polarity as the polarity of the toner particles in said developer material.
 6. Apparatus according to claim 5, said magnetic means being adjustably positioned within said applicator member to permit selective positioning of said magnetic means in relation to said platen means. 